The principal investigator will intensify and expand his basic research on the cognitive events that precede and allow for the performance of voluntary movements, and he will apply the research to the analysis of movement disorders. Toward fulfillment of the clinical objective, he will audit courses and engage in clinical research with two or more neurologists. Five projects will be pursued: (1) Planning of aimed hand movements. The aim of this new experimental procedure is to determine how people plan a series of aimed hand movements immediately after seeing a display specifying the targets to which movements must be aimed. (2) Cognitive control of movement sequences. This project is the proposed renewal of the Pl's NSF grant and consists of two parts: (a) The three-dimensional analogue of project (1) above, where the focus is on planning reaching and manipulation, both in normal and clinical (especially apraxic) populations; (b) Analysis of two recently discovered motor "illusions" that shed light on the mechanisms of serial ordering of behavior. (3) Internal representation of the body surface. By having subjects perform a new speeded discrimination task in which all possible pairs of test sites serve as targets and distractors, the data can be analyzed with multidimensional scaling to allow for "visualization" of the body representation. Pilot work has turned up effects of handedness and posture. (4) A book. A textbook, "Human Movement Control," will be written. The book will provide an overview of research and treatment pertaining to each of the major activity systems (e.g., Walking, Looking, Speaking, Writing, Reaching and Grasping. (5) Cognitive Darwinism. Darwin's theory of natural selection will be applied to cognitive function. The key notion is that spontaneous variation in cognitive structures may provide a basis for generalization, preparation, and other important phenomena.